U.S. patent number 7,918,210 [Application Number 12/844,624] was granted by the patent office on 2011-04-05 for method for determining valve degradation.
This patent grant is currently assigned to Ford Global Technologies, LLC. Invention is credited to Michael Damian Czekala, Jeffrey Allen Doering, Alex O'Connor Gibson, James Donald McCoy, Nelson William Morrow, Jr..
United States Patent |
7,918,210 |
Gibson , et al. |
April 5, 2011 |
Method for determining valve degradation
Abstract
A method for determining degraded valve operation. According to
the method, valve degradation can be determined from the duration
of a spark event. This method allows for the determination of both
intake and exhaust valve degradation.
Inventors: |
Gibson; Alex O'Connor (Ann
Arbor, MI), Doering; Jeffrey Allen (Canton, MI), Morrow,
Jr.; Nelson William (Saline, MI), McCoy; James Donald
(Flat Rock, MI), Czekala; Michael Damian (Canton, MI) |
Assignee: |
Ford Global Technologies, LLC
(Dearborn, MI)
|
Family
ID: |
40431180 |
Appl.
No.: |
12/844,624 |
Filed: |
July 27, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20100288037 A1 |
Nov 18, 2010 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
11851424 |
Sep 7, 2007 |
7762237 |
|
|
|
Current U.S.
Class: |
123/481; 701/114;
123/198F |
Current CPC
Class: |
G01M
15/042 (20130101); F01L 1/34 (20130101); F01L
13/0005 (20130101); F01L 2800/11 (20130101); F02P
2017/121 (20130101) |
Current International
Class: |
F02F
7/00 (20060101) |
Field of
Search: |
;123/198F,481,625
;701/101,107,114,115 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Kwon; John T
Attorney, Agent or Firm: Lippa; Allan J. Alleman Hall McCoy
Russell & Tuttle LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
The present application is a continuation of U.S. patent
application Ser. No. 11/851,424, filed on Sep. 7, 2007, entitled
"Method for Determining Valve Degradation" the entire contents of
which are incorporated herein by reference.
Claims
The invention claimed is:
1. A method to determine degradation of a cylinder exhaust valve of
an engine cylinder, comprising: initiating a spark event in the
cylinder after deactivating an intake valve of the cylinder; and
indicating exhaust valve degradation in response to at least a
duration or breakdown voltage of said spark event.
2. The method of claim 1 valve degradation is assessed by relating
the duration of the spark event to cylinder pressure, and relating
cylinder pressure to exhaust valve position.
3. The method of claim 2 wherein the exhaust valve is commanded
closed during the determination of exhaust valve degradation, where
the cylinder pressure indicates whether the exhaust valve is in a
desired closed position at a particular crankshaft interval.
4. The method of claim 1, wherein exhaust valve degradation is
assessed before fuel is injected during cylinder reactivation.
5. The method of claim 4 wherein the spark event is initiated
during an exhaust stroke.
6. The method of claim 4 wherein if spark duration indicates that
cylinder pressure is higher than expected, exhaust valve
degradation is identified, where subsequent fuel injection is based
on whether exhaust valve degradation is identified.
7. A method to determine degradation of an exhaust valve of an
engine cylinder, comprising: initiating a spark event in the
cylinder during an exhaust stroke and while the cylinder is
deactivated; and indicating valve degradation from flyback voltage
produced by said spark event.
8. The method of claim 7 further comprising filtering and
converting said flyback voltage to a digital signal for determining
a spark duration or breakdown voltage of said spark event.
9. The method of claim 7 wherein said valve degradation is
comprised of the exhaust valve not following a desired
trajectory.
10. The method of claim 7 wherein said deactivation include holding
an intake valve of the cylinder closed.
11. A method to determine degradation of a variable event
valvetrain, the method comprising: inducting an amount of air into
at least one cylinder during a combustion cycle; deactivating said
at least one cylinder after inducting said amount of air; providing
an indication of at least a degraded exhaust valve operable in said
cylinder, said indication provided after deactivating said at least
a cylinder; and said indication produced, at least in part, from
flyback voltage of an ignition coil during an exhaust stroke.
12. The method of claim 11 wherein said flyback voltage is
evaluated to determine the spark duration or breakdown voltage.
13. The method of claim 11 wherein said at least one cylinder is
deactivated by commanding at least an intake valve to a closed
position for at least a cycle of said cylinder.
14. The method of claim 11 wherein said internal combustion engine
is coupled to a hybrid powertrain.
15. The method of claim 11 wherein said air is inducted based an
intake throttle.
16. The method of claim 11 wherein the exhaust valve is deactivated
by a cam profile switching device before said indication.
17. The method of claim 16 further comprising deactivating fuel
flow to said at least one cylinder before the end of said
combustion cycle.
18. The method of claim 17 wherein said cylinder is deactivated, at
least in part, by changing the state of a cam profile switching
device.
Description
FIELD
The present description relates to a method for improving
recognition of valve degradation for an internal combustion engine
having a variable event valvetrain. The method may be particularly
useful for vehicles that utilize cylinder deactivation.
BACKGROUND
One method to determine valve degradation in an internal combustion
engine is described in U.S. Pat. No. 6,499,470. This method
presents a method for determine degradation of a cylinder halting
mechanism based on the rate of change in intake manifold pressure.
If the manifold pressure rate of change is low, fuel flow can be
stopped to the one or more cylinders.
The above-mentioned method can also have several disadvantages.
Specifically, the method does not appear to be capable of
determining a condition where operation of an exhaust valve
degrades while intake valves are deactivated. For example, if
intake and exhaust valves are commanded to closed positions to
deactivate a cylinder, intake manifold pressure will not be
affected by exhaust valve degradation because the intake valve
isolates the intake manifold from conditions in the cylinder and
exhaust system. As a result, the rate of change of intake manifold
pressure will not be affected by operation of the exhaust valve.
Consequently, the method does not appear to be able to diagnose
exhaust valve degradation from at least an attribute of said spark
event. This method overcomes at least some of the disadvantages of
the prior art.
Valve degradation can be assessed by determining the duration of an
ignition spark in a cylinder. Spark duration (i.e., the length of
time from the beginning of a spark to the end of a spark) can be
related to cylinder pressure and cylinder pressure can be related
to the position of a valve at a particular crankshaft angle.
Alternatively, breakdown voltage may be used as an indication of
cylinder pressure. Consequently, spark duration and/or breakdown
voltage can be used to determine the position and/or operation of a
valve at a particular crankshaft angle, thereby allowing the
determination of valve degradation.
During cylinder deactivation, it is common to deactivate a cylinder
by closing all valves operating in a cylinder. The valves are
closed to reduce engine pumping losses and to limit oxygen flow to
the exhaust system after treatment devices. Exhaust gases can be
trapped in deactivated cylinders to act as a spring, storing and
releasing rotational energy in the cylinder. However, if an exhaust
valve stays open or opens and closes during a cycle when valve
deactivation is desirable, the benefit of cylinder deactivation can
be reduced. The present method permits a spark to be initiated in a
cylinder during a scheduled cylinder deactivation period to
determine if the cylinder pressure indicates that an exhaust valve
is in a desired position at a particular crankshaft interval. This
allows determination of exhaust valve degradation when intake
valves are deactivated in a closed position.
Further, the method can be used to determine if an exhaust valve is
in a desired position during an exhaust stroke so that exhaust
valve degradation can be assessed before fuel is injected to a
cylinder during cylinder reactivation. For example, a spark event
can be initiated in a cylinder during an exhaust stroke while
exhaust valves are scheduled to open. If the spark duration
indicates that cylinder pressure is higher than expected, exhaust
valve degradation may be determined. If the spark duration
indicates that cylinder pressure is near an expected value, then it
may be determined that the exhaust valve is not degraded. The
exhaust valve evaluation may then be used to determine whether or
not it is desirable to inject fuel to the cylinder.
The present description may provide several advantages. In
particular, the approach may enable rapid and reliable evaluation
of both intake and exhaust valves. By ingeniously linking
attributes of a spark event to valve degradation, the inventors
herein have developed an inexpensive and reliable method to
determine valve degradation. In this regard, the method may also
help reduce engine emissions if valve degradation occurs. Further,
the method does not require pressure transducers or other function
specific transducers; it simply uses an existing spark plug to make
a determination of valve degradation. As such, the system and
method may be implemented at a low cost.
The above advantages and other advantages, and features of the
present description will be readily apparent from the following
Detailed Description when taken alone or in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The advantages described herein will be more fully understood by
reading an example of an embodiment, referred to herein as the
Detailed Description, when taken alone or with reference to the
drawings, wherein:
FIG. 1 is a schematic diagram of an engine;
FIG. 2 is a flow chart of an example cylinder valve degradation
strategy;
FIG. 3 is another flow chart of an example valve degradation
strategy;
FIG. 4 is an example plot of a cylinder deactivation and
reactivation wherein valve degradation is evaluated;
FIG. 5a is a plot that illustrates cylinder pressure during
cylinder deactivation without valve degradation;
FIG. 5b is a plot that provides one example of cylinder pressure
during cylinder deactivation when valve degradation is present;
FIG. 6a is a plot that illustrates cylinder pressure during
cylinder activation without valve degradation;
FIG. 6b is a plot that provides one example of cylinder pressure
during cylinder reactivation when valve degradation is present;
and
FIG. 7 is a plot that illustrates the influence that cylinder
pressure has on spark duration.
DETAILED DESCRIPTION
Referring to FIG. 1, internal combustion engine 10, comprising a
plurality of cylinders, one cylinder of which is shown in FIG. 1,
is controlled by electronic engine controller 12. Engine 10
includes combustion chamber 30 and cylinder walls 32 with cam shaft
130 and piston 36 positioned therein and connected to crankshaft
40. Combustion chamber 30 is known communicating with intake
manifold 44 and exhaust manifold 48 via respective intake valve 52
an exhaust valve 54. Intake valve 52 and exhaust valve 54 may be
selectively activated and deactivated using a lost motion device
(not shown) or alternatively by electric and/or hydraulic
actuators. Fuel injector 66 is shown having a nozzle capable if
injecting fuel directly into combustion chamber 30 in an amount in
proportion to the pulse width of signal FPW from controller 12.
Alternatively, fuel may be injected to the intake valve port
upstream of intake valve 52. Fuel is delivered to fuel injector 66
by fuel system (not shown) including a fuel tank, fuel pump, and
fuel rail (not shown). Intake manifold 44 is also shown
communicating with throttle body 58 via throttle plate 62.
Distributorless ignition system 88 provides ignition spark to
combustion chamber 30 via spark plug 92 in response to controller
12. Ignition system 88 contains circuitry (not shown) that is
capable of determining the peak breakdown voltage and duration of
ignition spark (i.e., the time that the spark arcs between two
elements, such as a spark plug electrode). The breakdown voltage
and ignition spark duration are made available (breakdown voltage
and spark duration may be analog or digital in character) to
controller 12. Two-state exhaust gas oxygen sensor 76 is shown
coupled to exhaust manifold 48 upstream of catalytic converter 70.
Alternatively, a Universal Exhaust Gas Oxygen (UEGO) sensor may be
substituted for two-state sensor 76. Two-state exhaust gas oxygen
sensor 98 is shown coupled to exhaust pipe 49 downstream of
catalytic converter 70. Sensor 76 provides signal EGO1 to
controller 12.
Controller 12 is shown in FIG. 1 as a conventional microcomputer
including: microprocessor unit 102, input/output ports 104, and
read-only memory 106, random-access memory 108, and a conventional
data bus. Controller 12 is shown receiving various signals from
sensors coupled to engine 10, in addition to those signals
previously discussed, including: engine coolant temperature (ECT)
from temperature sensor 112 coupled to cooling sleeve 114; a
measurement of manifold absolute pressure (MAP) form pressure
sensor 122 coupled to intake manifold 44; throttle plate position
from sensor 69, a measurement (ACT) of engine air amount
temperature or manifold temperature from temperature sensor 117; a
cam position signal (CAM) from a variable reluctance cam sensor
150; and a crankshaft position signal (CPS) from a variable
reluctance sensor 118 coupled to a crankshaft 40, and an engine
torque demand sensor 119. Alternatively, other types of sensors may
be substituted for the above-mentioned sensor type (e.g., Hall
sensors or optical sensors may be used in place of variable
reluctance sensors). Controller 12 storage medium read-only memory
106 can be programmed with computer readable data representing
instructions executable by processor 102 for performing the methods
described below as well as other variants that are anticipated but
not specifically listed.
Referring to FIG. 2, a flow chart of an example cylinder
deactivation strategy is shown. The strategy determines if valve
degradation is present during cylinder deactivation. If so, the
routine can take mitigating action, if desired.
In step 202, the routine determines if cylinder deactivation is
desired. A cylinder or a group of cylinders may be deactivated when
engine operating conditions indicate that engine operating
efficiency can be improved while the engine is operating with less
than its full complement of cylinders. This determination can be
made by assessing engine operating conditions such as operator
torque demand, engine temperature, engine speed, and signals alike.
The state of each operating condition can be evaluated in
conjunction with the other operating conditions (e.g., using
Boolean logic or state machines) to make a determination of whether
or not cylinder deactivation is desired. If cylinder deactivation
is desired, the routine proceeds to step 204. Otherwise, the
routine proceeds to exit.
In step 204, the routine completes intake events and combusts fuel
in the cylinders to be deactivated. One example of this sequence is
illustrated in FIG. 4. The routine determines how many cylinders
are to be deactivated and the specific cylinders that will be
deactivated. Cylinders are deactivated such that the engine remains
in an even firing mode. For example, if two cylinders of a four
cylinder are deactivated, cylinders one and four remain active such
that the engine combusts and air-fuel mixture every 360 crankshaft
degrees. On the other hand, cylinders two and three could remain
active instead of cylinders one and four. This would also allow the
engine to combust an air-fuel mixture every 360 crankshaft degrees
as well. The number of active cylinders is determined, at least in
part, by the desired engine torque demand. The specific cylinders
to be deactivated may be determined by logic or a state machine,
for example. Alternatively, the same group of cylinders may be
repeatedly activated and deactivated.
Once a cylinder is selected for deactivation, the routine controls
cylinder valves and fuel such that cylinders being deactivated
enter the deactivated state with exhaust gases trapped in the
cylinder. For example, where a cylinder is partially through an
intake stroke when cylinder deactivation is initiated, the intake
stroke is completed, combustion occurs, and the exhaust valves
remain closed to trap the exhaust gases in the cylinder, see FIG. 4
for example. If on the other hand, the cylinder is partially
through its exhaust stroke, the cylinder can complete another
intake stroke and combustion event before reaching the deactivated
state, if desired. The routine proceeds to step 206.
In step 206, the exhaust valves are deactivated. Exhaust valves may
be deactivated using lost motion mechanical devices that stop valve
movement by collapsing part of the actuator, by deactivating
electrical valves, cam profile switching devices, or by other known
methods. As mentioned in step 204, exhaust valves are deactivated
such that exhaust remains trapped in the cylinder. The routine
proceeds to step 208.
Note that valve deactivation/reactivation may not occur immediately
after the valve deactivation/activation command has been issued.
For example, if lost motion devices are used to deactivate/activate
a cylinder, the devices may be configured to move in relation to
camshaft position. Consequently, if a voltage is supplied to a
solenoid that controls oil flow to the lost motion device, the lost
motion device cannot immediately deactivate/reactivate the valve
while the lost motion device is being acted upon by the camshaft
because the oil pressure is not significant enough to overcome the
force being applied by the camshaft. In this case there will be a
latency period between the time the deactivation/reactivation
command is issued and when the valve is
reactivated/deactivated.
In step 208, a spark is initiated and the spark event attributes
are evaluated. The inventors herein have discovered that attributes
or characteristics of a spark event can be related to pressure in a
cylinder. In one example, the duration of a spark event can be
correlated to pressure in a cylinder. In particular, shorter
duration spark events indicate higher cylinder pressures while
longer duration spark events indicate lower cylinder pressures, see
FIG. 7 for example. The pressure/spark duration relationship can be
attributed to the effect cylinder pressure has on the spark plug
breakdown voltage. Lower cylinder pressure also indicates a lower
spark plug gap breakdown voltage, and higher cylinder pressure
indicates higher spark plug gap breakdown voltage.
In one example, spark is initiated by allowing current to flow to
the primary side of an ignition coil and then interrupting the
current flow. When the current flow is interrupted to the primary
coil, the magnetic field linking the primary and secondary coils is
disturbed and causes the voltage in the secondary coil to increase.
The voltage can reach a level that causes a spark to occur at a
spark plug that is attached to the secondary side of the ignition
coil.
A spark can be generated after a combustion event during the
exhaust stroke to determine if the exhaust valves have remained in
the closed position as commanded in step 206. The spark may be
initiated at a selected position between when the piston is at
bottom-dead-center (BDC) and top-dead-center (TDC). In one example,
a spark is initiated between .+-.45 crankshaft degrees of TDC
exhaust stroke. In another example, a spark is initiated between
.+-.10 crankshaft degrees of TDC exhaust stroke. An in yet another
example, a spark is initiated at substantially TDC (i.e., .+-.1
TDC) exhaust stroke. By initiating the spark event closer to TDC
exhaust stroke, a higher level of differential pressure can be
created such that a better signal to noise ratio results. For
example, if an exhaust valve is commanded to deactivate in a closed
position, but remains open during a portion of the exhaust stroke,
the pressure in the cylinder at TDC exhaust stroke approaches
atmospheric pressure. On the other hand, if the exhaust valve
deactivates in the closed position as commanded, the cylinder
pressure will be greater than atmospheric pressure and can
therefore provide a stronger indication that valve operation has
not degraded. And since the spark event duration is affected by the
cylinder pressure, the duration or length of time of the spark
event can be used to determine if the exhaust valve operation has
degraded.
The spark event duration can be determined in a variety of ways. On
method is described in U.S. Pat. No. 7,124,019 which is hereby
fully incorporated by reference for all purposes. In this method
the spark event duration is determined by monitoring the flyback
voltages of the primary ignition coil. The flyback voltage is
created by the occurrence of a spark jumping the electrode of a
spark plug that is coupled to the secondary coil of an ignition
coil. The flyback voltage is converted into a voltage pulse that is
related to the spark duration. In another embodiment, flyback
voltage on the primary side of an ignition coil can be monitored to
determine breakdown voltage. And breakdown voltage can be related
to cylinder pressure, see FIG. 7 for example. The routine proceeds
to step 210.
In step 210, the routine determines if exhaust valve degradation is
present. Each cylinder being deactivated undergoes a valve
degradation evaluation. In one example, the length of time of the
spark event is used to determine valve degradation, although
measures other than time are also anticipated, crankshaft degrees
for example. The duration of the spark determined from flyback
voltage in step 208 is compared to a predetermined spark duration
that has been stored in engine controller memory. If the spark
duration determined in step 208 exceeds the predetermined spark
duration then valve degradation is determined and the routine
proceeds to step 224. Alternatively, if breakdown voltage
determined from flyback voltage is below a predetermined level,
valve degradation can also be determined. Otherwise, the routine
proceeds to step 212.
In step 224, the routine determines if a predetermined number of
exhaust valve deactivation attempts have been exceeded. If so, the
routine proceeds to step 226. If not, the routine proceeds to step
204 where the cylinder that exhibited exhaust valve degradation
attempts the cylinder deactivation process again. Specifically,
since the cylinder has been exhausted, an additional intake and an
additional compression strokes are performed so that the cylinder
may be deactivated with exhaust gases in the cylinder.
In step 226, the routine sets an exhaust valve degradation flag to
indicate valve degradation. This flag may be used to inhibit fuel
flow and spark to the cylinder experiencing valve degradation if
desired. The routine proceeds to exit after the flag is set.
In step 212, intake valves are deactivated. Note that commands to
deactivate intake and exhaust valves may occur simultaneously or
commands may be issued to deactivate intake valves before exhaust
valves without deviating from the scope or intent of this
description. In one example, intake valve deactivation occurs in
the sequence illustrated by FIG. 4 where exhaust gases are trapped
in the cylinder during cylinder deactivation. In particular, the
intake valves open during the last combustion cycle prior to
cylinder deactivation while the exhaust valves remain closed.
Commands are issued to deactivate intake valves and then the
routine proceeds to step 214.
Note in another embodiment it is also possible to deactivate a
cylinder with fresh charge or an inducted air amount. In this
embodiment, exhaust valves are commanded closed after exhausting
cylinder contents. The cylinder can be reactivated by combusting at
least a fraction of the air that was inducted during the cylinder
deactivation process (i.e., combustion can be resumed using the air
trapped in the cylinder or intake valves may be activated before
exhaust valves to provide fresh air to the cylinder), and then the
exhaust valves can resume operation.
In step 214, a spark event is initiated and the spark duration is
determined. Step 214 is performed in the same manner as step 208,
but the crankshaft angle where the spark is initiated is different.
Since intake valves are typically opened during a portion of the
intake and compression strokes, a spark is initiated in one of
these strokes. In one example, a spark is initiated between .+-.45
crankshaft degrees from BDC intake stroke. In another example, a
spark is initiated between .+-.10 crankshaft degrees from BDC
intake stroke. In still another example, a spark is initiated at
substantially BDC (i.e., .+-.1 crankshaft degree) intake stroke. By
initiating a spark in the region of BDC intake stroke,
determination of an open intake valve can be improved. If an intake
valve is open when exhaust gases are present in a cylinder, a
portion of the exhaust gases will be vented to the intake manifold,
thereby lowering the cylinder pressure. The cylinder pressure is
likely to be lowest when the piston reaches BDC because the intake
valve is likely to have been open for some time and because the
cylinder volume is greatest near BDC. Therefore, the spark duration
can be evaluated at this crankshaft interval to assess intake valve
degradation. The routine proceeds to step 216.
In step 216, the routine determines if intake valve degradation is
present. Again, each cylinder being deactivated undergoes a valve
degradation evaluation. The intake valve degradation evaluation
routine also uses the length of time of the spark event to
determine valve degradation. The duration of the spark determined
in step 214 is compared to a predetermined spark duration that has
been stored in engine controller memory. If the spark duration
determined in step 214 is shorter than some predetermined spark
duration, then valve degradation is determined and the routine
proceeds to step 218. Otherwise, the routine proceeds to exit.
Alternatively, breakdown voltage can be substituted for spark
duration if desired.
In step 218, the routine determines if a predetermined number of
intake valve deactivation attempts have been exceeded. If so, the
routine proceeds to step 222. If not, the routine proceeds to step
220.
In step 220, exhaust valves are reactivated and the cylinder is
evacuated of exhaust gases before the routine proceeds to step 204.
By reactivating the exhaust valves, exhaust gases are released to
the exhaust manifold rather than the intake manifold. This allows a
fresh air charge to be inducted into the cylinder so that another
combustion event can occur before another cylinder deactivation
attempt.
In step 222, the routine sets an intake valve degradation flag to
indicate valve degradation. The flag is a software variable that
may also be used to inhibit fuel flow and spark to the cylinder
experiencing valve degradation if desired. Further, the flag may be
used to notify the operator or other vehicle systems, a hybrid
powertrain controller for example, that valve degradation has
occurred. The routine proceeds to exit after the flag is set.
Note that the spark events described in steps 208 and 214 may
utilize a single spark or multiple spark events may be used over a
range of crankshaft angles if desired. For example, a spark may be
initialized at 10 crankshaft angle degrees before TDC exhaust
stroke and 5 crankshaft angle degrees after TDC exhaust stroke to
determine exhaust valve degradation, if desired.
Referring now to FIG. 3, a flow chart of an example cylinder
reactivation strategy is shown. The strategy determines if valve
degradation is present during cylinder reactivation. If so, the
routine can take mitigating action.
In step 302, the routine determines if cylinder reactivation is
desired. In one example, a cylinder or a group of cylinders may be
reactivated when engine operating conditions indicate that an
increase in engine performance is desired. This determination can
be made by assessing engine operating conditions such as operator
torque demand, engine temperature, engine speed, and signals alike.
The state of each operating condition can be evaluated in
conjunction with the other operating conditions (e.g., using
Boolean logic or state machines) to make a determination of whether
or not cylinder reactivation is desired. If cylinder reactivation
is desired, routine proceeds to step 304. Otherwise, the routine
proceeds to exit.
In step 304, the routine reactivates each exhaust valve that has
been deactivated. Alternatively, selected exhaust valves may be
reactivated. Exhaust valves are reactivated (i.e., commanded to be
allowed to open and close during a cylinder cycle) before intake
valves so that the cylinder expels exhaust gases before an intake
event. This allows a cylinder to restart with a fresh cylinder air
charge and it limits the amount of EGR that may be pushed back into
the intake manifold. Note that the valve reactivation signals may
commence simultaneously, or they may occur at separate times, but
the exhaust valves are opened first due to mechanical limitations
or signal timing so that exhaust gases are expelled from the
cylinder. The routine proceeds to step 306.
In step 306, a spark is initiated and the spark duration is
evaluated. A spark is generated in the region where the piston
reaches TDC exhaust stroke to determine if the exhaust valves have
remained in the closed position in opposition to the commanded
issued in step 304. As described in the description of FIG. 2,
spark duration and/or breakdown voltage can be related to cylinder
pressure, and cylinder pressure during a specific crankshaft angle
interval can be related to valve operation. In one example, a spark
is initiated between .+-.45 crankshaft degrees of TDC exhaust
stroke. In another example, a spark is initiated between .+-.10
crankshaft degrees of TDC exhaust stroke. An in yet another
example, a spark is initiated at substantially TDC (i.e., .+-.1
TDC) exhaust stroke. By initiating the spark event closer to TDC
exhaust stroke, cylinder pressure at a crankshaft angle that is
closer to a higher potential pressure region can be compared
against atmospheric pressure. That is, if the exhaust valve opens
as instructed, the pressure in the cylinder will approach
atmospheric pressure, and as such, can be distinguished from a
higher exhaust gas pressure or from a lower cylinder vacuum. The
spark duration and/or breakdown voltage can be determined as
described in FIG. 2. The routine proceeds to step 308.
In step 308, the routine determines if exhaust valve degradation is
present. A comparison can be made between spark duration/breakdown
voltage made at atmospheric pressure and the spark
duration/breakdown voltage at a selected crankshaft location. The
spark duration/breakdown voltage measured at a specific crankshaft
interval in step 306 may be subtracted by the spark
duration/breakdown voltage expected at atmospheric pressure. The
difference in spark duration/breakdown voltage provides an
indication of the cylinder pressure difference, and thus allows the
routine to determine if the valves have allowed the cylinder to
evacuate and approach atmospheric pressure. If the difference
exceeds a predetermined amount, which may indicate a higher or
lower cylinder pressure, then exhaust valve degradation is
determined. If valve degradation is determined the routine proceeds
to step 322. If valve degradation is not determined the routine
proceeds to step 310.
In step 322, the routine determines if a predetermined number of
exhaust valve reactivation attempts have been exceeded. If so, the
routine proceeds to step 324. If not, the routine proceeds to step
304 where the cylinder that exhibited exhaust valve degradation
attempts the cylinder/valve reactivation process again.
In step 324, the routine sets an exhaust valve degradation flag to
indicate valve degradation. This flag may be used to inhibit fuel
flow and spark to the cylinder experiencing valve degradation if
desired. The routine proceeds to exit after the flag is set.
In step 310, fuel injection is activated for port injection
engines. Fuel is activated in port injection engines before intake
valves are opened in the reactivation process so that fuel may be
injected to a closed intake valve to improve fuel mixing. If the
fuel is to be injected directly into a cylinder fuel injection can
be delayed until it has been determined whether or not intake
valves have resumed operation, see step 316. The routine proceeds
to step 312.
In step 312, intake valves are commanded to reactivate. Similar to
step 304, commands to reactivate intake valves may occur
simultaneously or commands may be issued to reactivate intake
valves before exhaust valves without deviating from the scope or
intent of this description. In this example, intake valves are
commanded so that they open in the time period after exhaust valves
have opened, see FIG. 4 for example. Commands are issued to
reactivate intake valves and then the routine proceeds to step
314.
In step 314, a spark event is initiated and the spark duration is
determined. Step 314 is performed in the same manner as in step 306
but the crankshaft angle where the spark is initiated is different.
Since intake valves are typically opened during a portion of the
intake and compression strokes, a spark is initiated in one of
these strokes. In one example, a spark is initiated between .+-.45
crankshaft degrees from BDC intake stroke. In another example, a
spark is initiated at between .+-.10 crankshaft degrees from BDC
intake stroke. In still another example, a spark is initiated at
substantially BDC (i.e., .+-.1 crankshaft degree) intake stroke. By
initiating a spark in the region of BDC intake stroke,
determination of an open intake valve can be improved. If an intake
valve does not open after the exhaust valve has opened, the
cylinder pressure will be lowered due to the expanding cylinder
volume as the piston moves toward BDC. The lower cylinder pressure
can affect the spark duration and breakdown voltage such that a
vacuum in the cylinder can be distinguished from a cylinder
pressure that is closer to atmospheric pressure. Specifically, the
breakdown voltage will decrease and the spark duration will
increase at lower cylinder pressures. The routine proceeds to step
316.
In step 316, the routine determines if intake valve degradation is
present. If the spark duration determined in step 314 exceeds the
predetermined spark duration, then intake valve degradation is
determined and the routine proceeds to step 320. Alternatively,
breakdown voltage may be used to determine intake valve degradation
by comparing the monitored voltage to a predetermined amount. If
intake valve degradation is not determined the routine activates
fuel delivery for port fuel injected engines and proceeds to exit
(Note that fuel is reactivated in port fuel injected engines by
this step).
In step 318, the routine determines if a predetermined number of
intake valve reactivation attempts have been exceeded. If so, the
routine proceeds to step 320. If not, the routine proceeds to step
312.
In step 320, the routine sets an exhaust valve degradation flag to
indicate valve degradation. This flag may be used to inhibit fuel
flow and spark to the cylinder experiencing valve degradation if
desired. The routine proceeds to exit after the flag is set.
Referring now to FIG. 4, an example valve timing sequence during a
cylinder deactivation event is shown. The illustrated sequence is a
simulation that represents cylinder valve events for a four
cylinder engine operating in a four-stroke cycle. Since it is
possible to achieve the various illustrated valve trajectories
present in the description using a variety of actuator types (e.g.,
electrically actuated, hydraulically actuated, and mechanically
actuated), the type or design of the actuator employed is not meant
to limit or reduce the scope of the description. In this example,
the trajectories represent possible trajectories for intake valves
that can mechanically deactivate (I1-I4) and exhaust valves that
can mechanically deactivate (E1-E4). The letter "O" near the left
margin indicates the valve opening region for the valve trajectory.
The letter "C" indicates the valve closing region for the valve
trajectory.
The intake and exhaust valve position histories go from the left to
the right hand side of the figure. The intake valve trajectories
are labeled I1-I4 while exhaust valve trajectories are labeled
E1-E4. The vertical markers along the valve trajectory paths
identify the top-dead-center and bottom-dead-center positions for
the respective cylinders. Vertical line 401 represents an example
of an indication of where in time a request to deactivate cylinders
has occurred, vertical line 403 indicates the cylinder reactivation
command position. Example engine fuel injection timing is indicated
by injector spray representations (e.g., 420) and engine spark
timing is indicated by an "*". Fuel injection timing for a direct
injected engine is shown, although the methods illustrated apply as
well to port injected engines. The valve timing and engine position
markers can be related to the piston position of each cylinder of
the engine (e.g., lines 410 and 412). Pistons 1 and 4 are in the
same positions in their respective cylinders while cylinders 2 and
3 are 180.degree. out of phase with cylinders 1 and 4.
After a request to deactivate cylinders at 401, the intake valves
of cylinder 2 and 3 complete their current cycle and are then shown
held closed until the cylinder reactivation request 403. The valves
may be held closed by lost motion devices that collapse and do not
provide sufficient force to overcome the valve spring when a cam
lobe passes the lost motion device. For electrically actuated
valves, current can be supplied to a closing coil, thereby holding
the valve in closed. In this example, the cylinder deactivation
request occurs during an intake event of cylinder two, and the
injection timing is performed when the intake valve of the
respective cylinder is closed. Cylinder number two intake valve is
shown finishing the induction event that is in progress when the
request to deactivate cylinders is received. However, as mentioned
above, it is also possible to shut the intake valve earlier after a
request to deactivate cylinders so that the cylinder charge is
reduced, if electrically actuated valves are used for example. The
last combustion event for the cylinders being deactivated is shown
in cylinder two since the intake valves of cylinder three are held
closed after the engine stop request.
In this example, the mechanically actuated exhaust valves of
cylinders two and three are also deactivated after the cylinder
deactivation request. The exhaust valves are closed such that gases
from the last combustion event prior to cylinder deactivation are
trapped within the respective cylinders. As mentioned above, the
trapped exhaust gases act as a spring storing and releasing energy
as the crankshaft rotates, thereby reducing deactivated cylinder
losses and oil consumption. The exhaust valves may be deactivated
by known mechanical deactivation devices.
Evaluation of exhaust valve degradation during cylinder
deactivation and is initiated at spark events 440 and 450. The
spark events are initiated at TDC cylinder two and three
respectively. This location offers a high signal to noise ratio in
terms of cylinder pressure verses atmospheric pressure. If the
exhaust valves were to continue to open and close in accordance
with the mechanical cam profile, exhaust pressure would approach
atmospheric pressure since the exhaust gases would have an
opportunity to pass the exhaust valve at this crankshaft angle
timing. Thus, the illustrated TDC locations provide locations that
reduce the possibility of observing near atmospheric cylinder
pressure when the valves are in the desired close position. Note
that the spark timing can be advanced or retarded from this
location to avoid evaluating exhaust degradation where valve
overlap may be encountered, if desired.
Evaluation of intake valve degradation occurs during cylinder
deactivation is initiated at spark events 442 and 452. The spark
events are initiated at BDC cylinder two and three. This location
is selected to evaluate the cylinder pressure at a position where
the intake valve would be open if it were to continue to operate in
accord with a typical intake valve schedule. If the valve continues
to operate, the BDC location will provide a position where cylinder
pressure is expected to be low. If the exhaust valves close as
desired and exhaust valve degradation is not determined, the
cylinder pressure will be above atmospheric pressure when the
intake valve is held closed since the cylinder mixture expands with
combustion. Consequently, if intake and exhaust degradation is not
present the cylinder pressure is expected to be above atmospheric
pressure, if there is intake valve degradation, the cylinder
pressure is expected to be below or near atmospheric pressure.
Therefore, the spark duration can be used to distinguish between
different modes of valve degradation.
After cylinder reactivation is requested 403, the sequence begins
with exhaust valve reactivation 430 and 432. Cylinder number two
exhaust valve is reactivated first in this sequence because of the
engine position where the reactivation request occurred; however,
if the reactivation request location were change, reactivation of
cylinder number three exhaust valve would lead the reactivation
sequence. As mentioned above, the exhaust valves are reactivated
first so that exhaust gases remaining in the cylinder is discharged
before a new air-fuel mixture is inducted into the cylinder. This
ensures cylinder reactivation and improves cylinder charge
consistency.
Exhaust valve degradation is assessed at spark events 444 and 454.
The spark events are generated at TDC exhaust for the respective
cylinders. This location provides an opportunity for exhaust gases
to be evacuated from the cylinders before the evaluation is made.
If the exhaust valves operate in accordance with four-cycle timing,
the cylinder pressure will approach atmospheric pressure since the
exhaust system is vented to atmosphere. If the exhaust valve
degradation occurs, the cylinder pressure can be higher than
atmospheric because the cylinder volume is at its lowest level.
Consequently, if the spark duration reflects a pressure that is
less than a predetermined pressure for the particular engine speed
and load, exhaust valve degradation can be determined.
Cylinder number two and three intake valves are reactivated at
valve opening events 460 and 462. If the intake valves open in
accord with four-stroke valve timing, air is inducted into the
cylinder and the cylinder pressure will be near atmospheric
pressure or lower. On the other hand, if the intake valves do not
open as scheduled, the cylinder pressure will decrease as the
piston approaches BDC where the cylinder volume is the greatest.
Thus, intake valve degradation can be evaluated during cylinder
reactivation based on the difference between observed cylinder
pressure and expected cylinder pressure. That is, if cylinder
pressure is lower than the expected cylinder pressure, intake valve
degradation can be determined because the cylinder pressure will be
lower.
Referring now to FIG. 5a, simulation results for a desired cylinder
deactivation sequence is shown. The sequence illustrates cylinder
pressure for a single cylinder that is deactivated. The Y-axis
identifies the cylinder pressure while the X-axis indicates time.
The last combustion event is indicated by the cylinder pressure
near label 501. The first deactivated cylinder pressure peaks 503
and 504 represent TDC compression and TDC exhaust locations
respectively for the deactivated cylinder. The peak cylinder
pressures decay with time as a portion of compressed exhaust gases
pass piston rings.
Referring now to FIG. 5b, simulation results for degraded valve
operation during cylinder deactivation is shown. Similar to FIG.
5a, the sequence illustrates cylinder pressure for a single
cylinder that is deactivated. However, in this figure, the effect
of valve degradation is shown. Label 505 identifies the last
combustion event cylinder pressure before the cylinder is
deactivated. Label 507 illustrates cylinder pressure when the
cylinder has been deactivated but where there is valve degradation.
Comparing FIG. 5a to FIG. 5b, the cylinder pressure after cylinder
deactivation in FIG. 5b is lower than that shown in FIG. 5a. The
difference can be attributed to an exhaust valve being open during
the exhaust stroke while the intake valves are held closed during
the cylinder cycle. Since the exhaust valves continue to operate in
four-stroke timing, the cylinder pressure is reduced. The
difference in cylinder pressure from FIG. 5a to FIG. 5b,
particularly at the first two times the cylinder reaches TDC,
allows a spark to be generated at the TDC location from which valve
degradation can be determined.
Referring now to FIG. 6a, simulation results for a desired cylinder
reactivation sequence is shown. Like FIGS. 5a and 5b, the sequence
illustrates cylinder pressure for a single cylinder, but in this
case, the cylinder is reactivated. The Y-axis identifies the
cylinder pressure while the X-axis indicates time. The last
deactivated cylinder pressure peak occurs at 601, then the cylinder
pressure increases in pressure pulse 603 indicating combustion has
commenced. Notice also that there appear to be one half the number
of pressure peaks as compared to before the cylinder was
reactivated. This is because a pressure peak occurs at every TDC
(intake and exhaust) when the intake and exhaust valves are
simultaneously closed. After the cylinder reactivates the peak
pressure occurs slightly after TDC due to the expansion of
combusted gasses, so only one pressure peak is indicated for each
cylinder cycle.
Referring now to FIG. 6b, simulation results for degraded valve
operation during cylinder reactivation is shown. Similar to FIG.
6a, the sequence illustrates cylinder pressure for a single
cylinder that is reactivated. However, in this figure, the effect
of valve degradation is shown. Label 610 identifies a pressure
pulse in the last cylinder cycle before the cylinder is
reactivated. Label 612 illustrates cylinder pressure when the
cylinder has been reactivated and is elevated due to combustion. If
exhaust valve degradation is evaluated as described in step 306 of
FIG. 3, it is possible to avoid this condition since spark could be
inhibited when exhaust valve degradation is determined.
Alternatively, a spark can be generated at the crankshaft angle
where the second pressure pulse occurs 614, and valve degradation
can be indicated by the spark duration that reflects the higher
cylinder pressure. The cylinder pressure pulses after label 614 are
at a level that reflects working intake valves an exhaust valves
that remain in the closed position. As a result, the cylinder
pressure is elevated from the level that it assumed before label
612 because air is being repeatedly inducted and compressed,
thereby maintaining a steady supply of air compressed in the
cylinder.
FIG. 7 is a plot that illustrates the influence that cylinder
pressure has on flyback voltage and spark duration. Curves 710,
712, and 714 are example flyback voltage traces monitored at a
switching device that controls current flow through the primary
side of an ignition coil. Each curve represents the flyback voltage
signature for an individual ignition coil. Three curves are shown
for illustration purposes.
The curves illustrate primary side ignition coil voltage that is
generated after current flow is stopped in the primary coil. When
current flowing to the primary coil is interrupted, the magnetic
field generated by the current collapses and voltage is increased
on the secondary side of the ignition coil. The increased secondary
coil voltage is reflected back to the primary coil and is
observable as shown in FIG. 7. Label 701 indicates where current
flow to the primary coil is interrupted and where the spark event
begins.
Curve 710 represents the voltage observed after spark is initiated
in a cylinder having low pressure. Label 703 points to the
breakdown voltage generated during the ignition event. The
breakdown voltage is the voltage at which a spark is produced
across the spark plug gap. Similarly, labels 705 and 707 refer to
breakdown voltages for spark events at increasingly higher cylinder
pressures. That is, the pressure in the cylinder where flyback
voltage curve 712 was generated is higher than the pressure at
which flyback voltage curve 710 was generated. Likewise, the
cylinder pressure at which flyback voltage curve 714 was generated
was higher than the cylinder pressure at which curve 712 was
generated. In this example, the breakdown voltages observed are
12.7 kV for curve 710, 17.6 kV for curve 712, and 18.8 kV for curve
714 when the ignition coils were charged to the same level. Each
voltage curve settles to a plateau after reaching the breakdown
voltage. This plateau represents the time that the spark arc is
sustained across the spark plug gap. Labels 706, 704, and 702
indicate the end of the spark event.
Notice that the breakdown voltage increases as cylinder pressure
increases. Also note that the spark duration is reduced as the
cylinder pressure increases. The higher the breakdown voltage, the
less energy is left in the coil to sustain the spark event.
Therefore, breakdown voltage and spark duration (i.e., the length
of time from initiating a spark event until the arc ceases) can be
used to determine cylinder pressure. In one embodiment, breakdown
voltage is determined by a level detecting circuit that outputs a
digital value corresponding to the determined breakdown voltage. In
another embodiment, the spark duration is determined by filtering
the flyback voltage and converting it into a digital signal capable
of being input to a microprocessor or similar device (e.g.,
programmable gate array). This can be accomplished by attaching a
high impedance tap to the primary ignition coil. The ignition coil
voltage can then be clamped by diodes or capacitors and input to a
Schmidt trigger level detecting device. The now digital signal may
be processed to determine the spark duration. Note: variations in
the filtering circuitry are anticipated; therefore, the specific
circuitry described herein is not intended to limit the scope or
breadth of this description.
As will be appreciated by one of ordinary skill in the art, the
routines described in FIGS. 2-3 may represent one or more of any
number of processing strategies such as event-driven,
interrupt-driven, multi-tasking, multi-threading, and the like. As
such, various steps or functions illustrated may be performed in
the sequence illustrated, in parallel, or in some cases omitted.
Likewise, the order of processing is not necessarily required to
achieve the objects, features, and advantages described herein, but
is provided for ease of illustration and description. Although not
explicitly illustrated, one of ordinary skill in the art will
recognize that one or more of the illustrated steps or functions
may be repeatedly performed depending on the particular strategy
being used.
This concludes the description. The reading of it by those skilled
in the art would bring to mind many alterations and modifications
without departing from the spirit and the scope of the description.
For example, I3, I4, I5, V6, V8, V10, and V12 engines operating in
natural gas, gasoline, diesel, or alternative fuel configurations
could use the present description to advantage.
* * * * *